JP2553433B2 - Method for removing nitrogen oxides in exhaust gas - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method in which an exhaust gas is brought into contact with a specific catalyst in the presence of a small amount of added hydrocarbons or oxygen-containing compounds, or hydrocarbons or oxygen-containing compounds present in the exhaust gas. , A method for removing nitrogen oxides in exhaust gas.

[0002]

2. Description of the Related Art Nitrogen oxides in various exhaust gases (hereinafter referred to as
Since "NOx") is harmful to health and may cause photochemical smog and acid rain, development of effective removal means thereof is desired.

Conventionally, several methods for reducing NOx in exhaust gas using a catalyst have been put into practical use as methods for removing NOx. For example, (a) a three-way catalytic method in a gasoline vehicle, and (b) a selective catalytic reduction method using ammonia for exhaust gas from a large facility discharge source such as a boiler. Other proposed methods include (c) NO in exhaust gas using hydrocarbons.
As a method for removing x, a method in which a metal oxide such as alumina supporting a metal such as copper is used as a catalyst and brought into contact with a gas containing NOx in the presence of hydrocarbon (JP-A-63-100, 91).
9 publication).

[0004]

SUMMARY OF THE INVENTION The method (a) is
Hydrocarbon components and carbon monoxide contained in automobile flue gas are made into water and carbon dioxide by a catalyst, and at the same time NOx
Is reduced to nitrogen, so that the amount of oxygen contained in NOx and the amount of oxygen required for oxidizing the hydrocarbon component and the carbon monoxide component are stoichiometrically equal to each other. Combustion needs to be adjusted, and in a system such as a diesel engine in which excess oxygen exists, there is a serious problem that it cannot be applied in principle.

Further, in the method (b), ammonia, which is extremely toxic and has to be handled as a high-pressure gas in many cases, is used, so that the handling is not easy and the equipment becomes huge, and a small exhaust gas is generated. It is technically extremely difficult to apply it to a source, especially a mobile source, and it is not economical.

On the other hand, the method (c) is mainly applied to gasoline automobiles, and it is difficult to apply it under the exhaust gas conditions of a diesel engine and the activity of the catalyst is insufficient. That is, since a metal such as copper is contained as a component of the catalyst, it is not only poisoned by sulfur oxides discharged from the diesel engine, but also the activity of the catalyst is deteriorated due to aggregation of the added metal. It is not suitable for the removal of NOx in exhaust gas from automobiles and has not been put to practical use.

The present invention has been made as a result of extensive studies on various problems existing in the above (a) to (c). Even in an oxidizing atmosphere, various kinds of equipment including exhaust gas of a diesel engine can be used. It is an object of the present invention to provide a method for efficiently removing NOx in exhaust gas even if the exhaust gas contains sulfur oxides.

[0008]

In order to solve the problems existing in the above conventional methods, the present inventors have previously used a catalyst obtained by treating a metal oxide with a compound having a sulfate group. Proposing a method (Japanese Patent Application No. 2-20410)
No. 2-20413), and as a result of further studies, use of a catalyst composed of a complex of a polyvalent metal sulfate or a fourth-period transition metal salt supported on the catalyst. As a result, they have found that NOx can be more effectively removed in exhaust gas containing sulfur oxides without causing a decrease in activity, and have completed the present invention.

That is, the method for removing nitrogen oxides in exhaust gas according to the present invention is carried out by impregnating oxides other than zeolite with a compound having a sulfate group in the presence of hydrocarbons or oxygen-containing compounds and then calcining. Sulfate-containing oxide ,
A catalyst comprising a polyvalent metal sulfate or a fourth-period transition metal salt supported thereon and an exhaust gas containing NOx are brought into contact with each other, and the catalyst and NOx are contained under the same conditions as above. It is also characterized in that the exhaust gas is brought into contact with the oxidation catalyst and then the gas is brought into contact with the oxidation catalyst.

Hereinafter, the details of the method of the present invention will be described together with the operation. In the present invention, sulfur which is one of the constituent components of the catalyst is used.
Acid radical-containing oxide, treatment with a compound having a sulfate group (sand
That is, it is an oxide (hereinafter referred to as a sulfate radical oxide ) obtained by baking after impregnating the compound, and specific examples of the oxide include:
Can be exemplified alumina - titanium oxide, zirconium oxide, hafnium oxide, iron oxide, tin oxide, alumina,及 beauty complex oxide containing one or more of these oxides, such as titania-zirconia, silica.

Specific examples of the compound having a sulfate group include:
Examples thereof include sulfuric acid and ammonium sulfate. In addition, any compound can be used as long as it produces a sulfate group on the oxide by the drying or baking treatment after the treatment.

Treatment of the oxide with a compound having a sulfate group, for example, sulfuric acid, is carried out by contacting the oxide with sulfuric acid at a specific temperature at room temperature, drying and then calcining in air at a specific temperature. In general, a more active catalyst can be obtained by treating an amorphous oxide, a hydroxide, a hydrous oxide or the like with a sulfuric acid in the same manner as a crystalline oxide.

The concentration of sulfuric acid used for the treatment varies depending on the kind of oxide, but it is usually about 0.01 to 10 mol / liter, preferably about 0.1 to 5 mol / liter, and the sulfuric acid having the concentration is used as a catalyst weight. About 5 to 20 times the amount is used, and it is brought into contact with the oxide. Further, when ammonium sulfate is used as a compound having a sulfate group, it can be treated in the same manner as above.

Examples of the polyvalent metal sulfate in the method of the present invention (hereinafter referred to as “sulfate”, unless otherwise specified, the sulfate means a polyvalent metal sulfate) include Group I in the periodic table. Group b, Group II, Group III, Group IV, Group V a Subgroup, Group VI a Subgroup, Group VII a Subgroup, Group VII
Sulfates of metals belonging to Group I, such as copper sulfate, magnesium sulfate, zinc sulfate, cadmium sulfate, barium sulfate, aluminum sulfate, zirconium sulfate, vanadium sulfate, chromium sulfate, manganese sulfate, iron sulfate and cobalt sulfate. A metal sulfate is illustrated. These sulfates may be used alone or in combination of two or more.

Further, examples of the fourth period transition metal salt in the method of the present invention (hereinafter, referred to as a metal salt, unless otherwise specified, the metal salt means a fourth period transition metal salt) include:
There are inorganic salts such as nitrates, ammonium salts, phosphates and halides of transition metals belonging to the 4th period in the periodic table, and organic acid salts such as acetates and oxalates. Specifically, copper nitrate, zinc phosphate, titanium chloride, ammonium vanadate, chromium nitrate, manganese nitrate, iron nitrate, iron oxalate, Fe (CO) ₅ , cobalt acetylacetonate, cobalt acetate, cobalt chloride, odor Examples thereof include cobalt iodide, cobalt iodide, nickel acetate and nickel nitrate. These metal salts may be used alone or in combination of two or more.

The method of supporting the sulfate or metal salt on the sulfate radical oxide is not particularly limited, and any conventionally known method can be used. That is, the sulfate radical oxide molded into powder or pellets is impregnated with an aqueous solution of a desired sulfate or metal salt, excess water is removed by filtration or evaporation, and dried, and if necessary, fired. Further, an aqueous solution of a desired sulfate or metal salt is added to the sulfate radical oxide, mixed well by a kneading treatment and the like, then dried, and baked if necessary.

For example, in the case of an insoluble sulfate such as barium sulfate, a water-soluble barium salt is selected, an aqueous solution of this water-soluble salt is mixed with a sulfate radical, and this is mixed with sulfuric acid or ammonium sulfate. A solution containing a sulfate ion such as that described above is used to deposit the sulfate salt on the sulfate radical oxide, or a method in which the sulfate radical oxide and the insoluble sulfate salt are mixed well by kneading treatment, etc. Can be supported on the substrate.

The amount of the sulfate or metal salt supported is not particularly limited, but if it is too large, the effect of the sulfate radical oxide is not exhibited, and if it is too small, the activity improving effect of the sulfate or metal salt is not exhibited. Generally, it varies depending on the type of sulfate, metal salt or sulfate, but in the case of sulfate, it is about 0.1 to 50 wt% or less, preferably about 1 to 20 wt%.
Within the range of about 0.01 to 50 wt% for metal salts,
Suitably, it is preferably within the range of about 0.1 to 20 wt%.

In order for the sulfate or metal salt-supported sulfate radical oxide prepared as described above to exhibit high catalytic activity,
In the process of preparing the sulfate radical oxide, it is preferable to perform the baking treatment in the process after the treatment with the compound having a sulfate radical. The firing treatment may be a usual firing treatment in air,
The optimum firing temperature in air is generally about 200 to 800 ° C, preferably about 300 to 700 ° C, although the optimum temperature varies depending on the type of sulfate radical oxide or the type of sulfate or metal salt used by supporting.

Further, the above catalyst can be used by supporting it on a so-called carrier. As the carrier, a commonly used inorganic carrier can be used and is not particularly limited, but in general, a carrier having a large surface area is preferable, and an alkaline carrier is not preferable. Specifically, an inorganic oxide, that is,
Al, La, Ce, Si, Ti, Zr, Th, Nb, T
Examples include oxides such as a and Cr, and composites of two or more thereof, such as silica alumina, silica titania, and alumina titania, and clay, such as kaolin, and natural products such as diatomaceous earth can also be used. Suitable examples include alumina, silica, chromia, silica-alumina and the like. These carrier substances may be used alone or in combination of two or more.

In these carriers, the sulfate or metal salt-supported sulfate radicals are well dispersed or synergized without impairing the catalytic properties of the sulfate or metal salt-supported sulfate radical oxides, and the catalyst activity and selection can be improved. It has the effects of improving the moldability, helping to remove the reaction heat, and improving the moldability. There is no particular limitation on the method for supporting the sulfate or the metal salt-supported sulfate radical oxide on the carrier, and a conventionally known method can be used.

The amount of sulfate or metal salt-supported sulfate radical supported in the case of using a carrier is not particularly limited, but if the amount is too large, the above-mentioned effect of the carrier is not exhibited.
If the amount is too small, the performance of the sulfate or metal salt-supported sulfate radical oxide as a catalyst will not be exhibited. Generally, about 1 to 8 for both sulfate-bearing sulfate radical oxide and metal salt-bearing sulfate radical oxide.
It is in the range of 0 wt%, preferably about 5 to 50 wt%.

The catalyst can be used in the form of powder, granules, pellets, honeycombs and the like. Its shape and structure do not matter. Further, when the catalyst is molded and used, a binder usually used at the time of molding, that is, clays such as bentonite, silica sol, polyvinyl alcohol, and the like,
Lubricants, that is, graphite, wax, fatty acid salt, carbowax and the like can be used.

The NOx-containing gas to be treated by the method of the present invention includes diesel engine exhaust gas from diesel vehicles and stationary diesel engines, gasoline engine exhaust gas from gasoline vehicles, exhaust gas from nitric acid production equipment and various combustion equipment. Can be mentioned. NOx in these exhaust gases
Is removed by bringing the catalyst into contact with exhaust gas in the presence of hydrocarbons or oxygen-containing compounds.

The above catalyst can reduce and decompose NOx even in a so-called reducing atmosphere in which oxygen does not exist so much.
NOx can be reduced and decomposed more efficiently in an oxidizing atmosphere. Here, the reducing atmosphere means that the carbon monoxide, hydrogen and hydrocarbons contained in the exhaust gas and the reducing substances such as hydrocarbons or oxygen-containing compounds added as necessary in the method of the present invention are completely oxidized. Then, it means an atmosphere containing less oxygen than the amount of oxygen necessary for converting into water and carbon dioxide.

The oxidizing atmosphere means an atmosphere containing oxygen in excess of the above-mentioned necessary oxygen amount. For example, in the case of exhaust gas discharged from an internal engine such as an automobile, the air-fuel ratio is large. It is a state (lean area) atmosphere,
Usually, the excess oxygen ratio is about 20 to 200%. In the oxidizing atmosphere, the catalyst preferentially promotes the reaction between the hydrocarbons or the oxygen-containing compound and NOx over the reaction between the hydrocarbons or the oxygen-containing compound and oxygen to remove NOx. .

The hydrocarbons or oxygen-containing compounds to be present, that is, the reducing substance for reducing and removing NOx may be particulates which are incomplete combustion products of hydrocarbons and fuels remaining in the exhaust gas, When the amount is insufficient to accelerate the above reaction, it is necessary to add hydrocarbons or oxygen-containing compounds from the outside.

The abundance of hydrocarbons and oxygen-containing compounds is not particularly limited. For example, when the required NOx removal rate is low, it may be smaller than the theoretical amount required for the reductive decomposition of NOx. However, since the reduction reaction proceeds more in excess of the required theoretical amount, it is generally preferable to make it exist in excess. Usually, about 20 to 2,000% of the theoretical amount required for the reductive decomposition of NOx, preferably Is about 30-1,500%
Too much.

Here, the necessary theoretical amount of hydrocarbons and oxygen-containing compounds means that oxygen is present in the reaction system, so that in the present invention, it is necessary to reduce and decompose nitrogen dioxide (NO ₂ ). It is defined as the amount of hydrocarbons and oxygen-containing compounds. For example, using propane as the hydrocarbons
The theoretical amount of propane is 200 ppm when reductively decomposing 000 ppm of nitric oxide (NO) in the presence of oxygen.
Generally, depending on the amount of NOx in the exhaust gas, the amount of carbon hydrogens and oxygen-containing compounds to be present is about 50 in terms of methane.
It is about 10,000 ppm.

As the reducing substance for reducing NOx by the catalyst of the present invention, any substance is effective as long as it is a carbon-containing substance such as a flammable organic compound, but from the practical point of view, nitrogen, sulfur and halogen are included. Compounds such as the above have many problems such as price, generation of secondary harmful substances, loss of catalyst, etc., and solid substances such as carbon black and coal, such as supply to the catalyst layer, contact with the catalyst, etc. In general, hydrocarbons and oxygen-containing compounds are preferable from the standpoint of point, and those of gas or liquid state from the viewpoint of supply to the catalyst layer, and those of gasification at the reaction temperature from the viewpoint of reaction are particularly preferable.

Specific examples of the hydrocarbons in the present invention include gaseous hydrocarbons such as methane, ethane, ethylene, propane, propylene, butane and butylene, and liquid hydrocarbons. Examples include single hydrocarbons such as pentane, hexane, octane, heptene, benzene, toluene and xylene, and mineral oil-based hydrocarbon oils such as gasoline, kerosene, light oil and heavy oil. Further, the oxygen-containing compound in the present invention means an oxygen-containing organic compound, alcohols such as methyl alcohol, ethyl alcohol, propyl alcohol, octyl alcohol, ethers such as dimethyl ether, ethyl ether, propyl ether, methyl acetate, acetic acid. Examples thereof include esters such as ethyl and fats and oils, and oxygen-containing organic compounds such as ketones such as acetone and methyl ethyl ketone. These hydrocarbons and oxygen-containing organic compounds may be used alone or in combination of two or more.

Unburned or incompletely burned products such as fuel existing in the exhaust gas, that is, hydrocarbons and particulates are also effective as the reducing agent and are included in the hydrocarbons of the present invention. This is because the catalyst of the present invention is
This means that it also has a function as a catalyst for reducing / removing hydrocarbons and particulates in exhaust gas.

The NOx-removing reaction in the method of the present invention is carried out by preparing a reactor in which the above catalyst is arranged, allowing hydrocarbons and oxygen-containing compounds to be present, and passing the NOx-containing exhaust gas. Regarding the reaction temperature at this time, the optimum reaction temperature varies depending on the type of the catalyst and hydrocarbons and oxygen-containing compounds, but a temperature close to the temperature of the exhaust gas is preferable because heating equipment for the exhaust gas is unnecessary, and generally about 200 to 800 ° C. , Preferably about 300-600 ° C. The reaction pressure is not particularly limited, and the reaction proceeds under pressure or under reduced pressure, but it is convenient to introduce the exhaust gas into the catalyst layer at a normal exhaust pressure to proceed the reaction. The space velocity is determined by the type of catalyst, other reaction conditions, the required NOx removal rate, etc., and is not particularly limited, but is generally about 500 to 100,000 hr ⁻¹ , preferably about 1,000 to 70,000 hr ^−. The range is ¹ . In the method of the present invention, when treating the exhaust gas from the internal combustion engine, it is preferable to arrange the exhaust gas downstream of the exhaust manifold.

When the exhaust gas is treated by the above-mentioned method of the present invention, depending on the treatment conditions, incomplete combustion products such as unburned hydrocarbons and carbon monoxide which cause pollution may be present in the treated gas. May be discharged. This problem can be solved by bringing the gas treated with the catalyst of the present invention (referred to as a reduction catalyst) into contact with the oxidation catalyst in an oxidizing atmosphere.

As the oxidation catalyst that can be used in the method of the present invention, generally, any catalyst that completely burns the above-mentioned incomplete combustion product may be used, and platinum may be added to a porous carrier such as activated alumina, silica or zirconia. , Noble metals such as palladium and ruthenium, base metal oxides such as lanthanum, cerium, copper, iron, molybdenum, and perovskite-type crystal structures such as cobalt lanthanum trioxide, lanthanum iron trioxide, and cobalt strontium trioxide. Examples thereof include those carried alone or in combination. In this case, the loading amount of the catalyst component is about 0.01 to the carrier for the noble metal.
It is about 2 wt% and about 5 to 7 for base metal oxides.
It is about 0 wt%. Of course, especially for base metal oxides,
It can also be used without being carried on a carrier. The additives to be added for the purpose of shape of the oxidation catalyst, molding, etc. are the same as those in the case of the reduction catalyst, and various kinds can be used.

The use ratio of the above reduction catalyst and oxidation catalyst,
The amount of the catalyst component supported on the oxidation catalyst can be appropriately selected according to the required performance, and particularly when the substance to be removed by oxidation is an intermediate oxide of a hydrocarbon such as carbon monoxide, the reduction catalyst and the oxidation can be used. Although it is possible to use a mixture with a catalyst, generally, the reduction catalyst is arranged on the exhaust gas upstream side and the oxidation catalyst is arranged on the exhaust gas downstream side.

As a specific example of purifying exhaust gas by using these catalysts, a reactor in which a reduction catalyst is arranged is arranged in an exhaust gas introduction section (first stage), and a reactor in which an oxidation catalyst is arranged is arranged in an exhaust gas discharge section (second stage). Then there is a method to use. Further, it is also possible to arrange and use each catalyst in one reactor at a ratio according to the required performance. The ratio of the reduction catalyst (A) to the oxidation catalyst (B) is generally expressed by (A) / (B) and used in the range of about 0.5 to 9.5 / 9.5 to 0.5.
The use temperature of the oxidation catalyst does not have to be the same as the use temperature of the reduction catalyst, but in general, it is particularly necessary to select the one that can be used within the range of the use temperature of the above-mentioned reduction catalyst, which requires heating and cooling equipment. Not preferred.

[0038]

EXAMPLES Next, examples of the method of the present invention will be given, but the method of the present invention is not limited to these examples. (1) Preparation of Catalyst-1 Examples 1 to 3 and Comparative Example 1 (Preparation of sulfate group-treated zirconium oxide) 10 g of commercially available zirconium hydroxide was placed on a paper, and 100 ml of 0.7 mol / liter sulfuric acid was flowed. Then, it was air-dried and then calcined in air at 550 ° C. for 3 hours to obtain sulfate group-treated zirconium oxide (hereinafter referred to as * zirconium oxide). This was used as the catalyst of Comparative Example 1.

(Preparation of Nickel Sulfate-Supported * Zirconium Oxide) The amounts of * zirconium oxide and nickel sulfate shown in Table 1 were weighed, and the nickel sulfate was dissolved in a small amount of water and impregnated into * zirconium oxide. Then, after evaporating and drying the water content, it was calcined in air at 400 ° C. for 2 hours to obtain each catalyst.

[0040]

[Table 1]

Examples 4 to 14, Comparative Example 2 (Preparation of Sulfuric Acid Root Treated Titanium Oxide) 1 liter of water was placed in a beaker and 1 kg of titanium tetrachloride was slowly dropped and dissolved while cooling with ice while stirring. Let Separately, 15
% 910 g of ammonia water was diluted with 570 g of cold water to prepare a solution, which was stirred with the above titanium tetrachloride solution,
It was added dropwise over 5 minutes. The temperature of the slurry after neutralization is 90
Above 8 ° C, PH is 8-9 and TiO ₂ conversion concentration is about 12.
It was 3%. The precipitate was separated by filtration, washed well with water, and dried to obtain titanium hydroxide (titanic acid). 10 g of this titanium hydroxide was placed on a paper filter, 100 ml of 0.7 mol / liter sulfuric acid was flown, and air-dried, and then 550 in air.
It was calcined at 3 ° C. for 3 hours to obtain sulfate-treated titanium oxide (hereinafter referred to as * titanium oxide). This was used as the catalyst of Comparative Example 2.

(Preparation of Sulfate Supported * Titanium Oxide) The amounts of sulfate and * titanium oxide shown in Table 2 were weighed, and the sulfate was dissolved in a small amount of water and impregnated into * titanium oxide. Next, water was evaporated and dried, and calcined in air at 400 ° C. for 3 hours to obtain each catalyst.

[0043]

[Table 2]

(2) NOx Removal Reaction-1 Examples 1-12, Comparative Examples 1-2 0.2 g of the catalyst prepared as described above (Examples 7 and 8)
Then, 0.1 g) was charged into an atmospheric flow type reactor, and 10 g
Nitrogen monoxide (hereinafter referred to as NO) at 00 ppm and 10%
Oxygen and 1000 ppm propylene (in Example 11, ethyl alcohol 600 ppm instead of propylene)
Helium gas (hereinafter called He) containing 60m / min
The reaction was carried out at a flow rate of 1 l. The analysis of the reaction gas is
It was performed using a gas chromatograph. The reductive decomposition rate of NO was determined from the yield of generated nitrogen, and the results are shown in Table 3 as Examples 1-12 and Comparative Examples 1-2.

[0045]

[Table 3]

Example 13 0.1 g of the catalyst of Example 8 was charged into a normal pressure flow reactor, and at 500 ° C., 1000 ppm NO and 1000 pp were added.
Propylene of m and He containing oxygen at the concentrations shown in Table 4 were fed at a flow rate of 60 ml / min to carry out the reaction. The analysis of the reaction gas and the reduction decomposition rate of NO were carried out in the same manner as in Example 8, and the results are shown in Table 4 as Example 13.

Example 14 Using 0.2 g of the catalyst of Example 10, the reduction decomposition rate of NO was determined in the same manner as in Example 13, and the results are shown in Table 4 as Example 14.

[0048]

[Table 4]

(3) Example of Disposing Oxidation Catalyst Downstream of Reduction Catalyst Example 15, Reference Example As the NO reduction decomposition catalyst, 0.2 g of the catalyst of Example 4 was placed upstream of the reactor, and unreacted hydrocarbons, etc. The reduction decomposition rate of NO was investigated in the same manner as in Example 4 except that 0.2 g of a commercially available 0.5% palladium-supported alumina catalyst as an oxidation catalyst was charged downstream. The results are shown in Table 5 together with the results when the oxidation catalyst was not filled for reference. As is clear from Example 15 and Reference Example in Table 5, when the oxidation catalyst was not charged, unreacted propylene and carbon monoxide, which is an incomplete combustion product, flowed out, but the oxidation catalyst was charged. In this case, it can be seen that only carbon dioxide, which is a complete oxide, is flowing out.

[0050]

[Table 5]

(4) Preparation of catalyst-2 Example 16, Comparative example 3 (Preparation of sulfate group-treated zirconium oxide) Commercially available zirconium hydroxide (100 g) was put on a paper, and 0.5 mol / liter of sulfuric acid (1500 ml) was flowed. Then, it was air-dried and then calcined in air at 550 ° C. for 3 hours to obtain sulfate group-treated zirconium oxide (hereinafter referred to as ** zirconium oxide). This was used as the catalyst of Comparative Example 3.

(Preparation of zirconium oxide supported on metal salt) 10.6 g of cobalt acetate [Co (O
The _{Ac) 2} · 4H 2 O] was dissolved in water 18 ml, was added ** zirconium oxide 50g was obtained by the above method in the solution, was impregnated with a metal salt. Then, after evaporating and drying the water content, it was calcined in air at 500 ° C. for 2 hours to obtain a catalyst.

Examples 17 to 20 and Comparative Example 4 Zirconium oxide obtained in Example 16 and various metal salts shown in Table 6 were weighed, and the metal salts were prepared in the same manner as in Example 16. * Supported on zirconium oxide to obtain various metal salt-supported catalysts.

[0054]

[Table 6]

Example 21, Comparative Example 4 100 g of the titanium hydroxide obtained in Examples 4 to 14 was placed on a paper roll, and 1500 ml of 0.5 mol / l sulfuric acid was flowed, followed by air drying, and then in air at 550 ° C. It was calcined for 3 hours to obtain sulfate group-treated titanium oxide (hereinafter referred to as ** titanium oxide). This was used as the catalyst of Comparative Example 4.

(Preparation of Titanium Oxide Bearing Metal Salt) 0.4 ml of cobalt acetate (tetrahydrate) as a metal salt in 20 ml
Was dissolved in water, and this was impregnated with 50 g of titanium oxide. Then, water was evaporated and dried, and calcined in air at 500 ° C. for 3 hours to obtain a catalyst. The amount of cobalt carried by this catalyst was 0.2 wt% in terms of metal.

(5) NOx removal reaction-2 Examples 16 to 21, Comparative Examples 3 to 4 The catalysts prepared as described above were charged in an atmospheric pressure flow reactor in the amounts shown in Table 7 to obtain 1000 ppm. NO and 10
He containing 100% oxygen and 1300 ppm propane was fed at a flow rate of 60 ml / min to carry out the reaction. Analysis of the reaction gas was performed using a gas chromatograph. The reductive decomposition rate of NO was determined from the yield of generated nitrogen, and the results are shown in Table 7 as Examples 16 to 21 and Comparative Examples 3 to 4.

[0058]

[Table 7]

[0059]

As described above in detail, according to the method of the present invention, in the presence of hydrocarbons and oxygen-containing compounds, sulfur oxides are contained in exhaust gas even in an oxidizing atmosphere in which oxygen is excessively present. Even if it is included, N in the exhaust gas is efficiently
Ox can be removed. This is because the catalyst according to the present invention reacts with NOx in the presence of hydrocarbons or oxygen-containing compounds more than with hydrocarbons or oxygen-containing compounds and oxygen. This is to promote it.

Further, the use of the catalyst according to the present invention may cause pollution problems such as unreacted or produced hydrocarbons, carbon monoxide, and other oxidation intermediate products which may be discharged depending on the reaction conditions. The volatile substances can be completely oxidized to carbon dioxide and water vapor. As described above, the method of the present invention is capable of efficiently removing NOx from exhaust gas from various facilities, including diesel engine exhaust gas, and has extremely high industrial value.

Front Page Continuation (72) Inventor Yoshiaki Kaneda, 1-1 Higashi, Tsukuba, Ibaraki Prefecture, Institute of Industrial Science and Technology (72) Inventor Hideaki Hamada, 1-1, East, Tsukuba, Ibaraki Institute of Chemical Technology, Institute of Industrial Technology (72) Inventor, Takehiko Ito, 1-1, Higashi, Tsukuba, Ibaraki, Institute of Chemical Technology, Institute of Industrial Technology (72) Inventor, Motoki Sasaki, 1-1, Higashi, Tsukuba, Ibaraki (72) Invention Suganuma Fujio 228-16 Shinjuku, Shinjuku, Showa-machi, Kita-Katsushika-gun, Saitama 228-16 (72) Inventor Akihiro Kitazume 2-15-36 Sugito, Sugito-cho, Kita-Katsushika-gun, Saitama Kazushi Usui 1-chome Iwana, Noda-shi, Chiba 62 10 (72) Inventor Tomohiro Yoshinari 3-32-25 Motomachi, Urawa-shi, Saitama (72) Inventor Mitsunori Tabata 1134-2, Gongendo, Satte City, Saitama Prefecture Tadao Nakatsuji, Ebisu Sakai, Osaka Prefecture 5-1, Shimamachi, Central Research Institute, Sakai Chemical Industry Co., Ltd. (72) Inventor Hiromasu Shimizu Sakai, Osaka 5-1, Ebishimacho Sakai Chemical Industry Co., Ltd. Central Research Institute (72) Inventor Ritsu Yasukawa 5-1, Ebishimacho Sakai City, Osaka Pref. Sakai Chemical Industry Co., Ltd. Central Researcher Naoto Noda (56) References JP 4-371216 (JP, A) JP 54-51990 (JP, A) JP 5-31326 (JP, A) JP 5-38420 (JP, A)

Claims (2)

(57) [Claims] 1. A sulfate group-containing oxide obtained by impregnating an oxide other than zeolite with a compound having a sulfate group in the presence of a hydrocarbon or an oxygen-containing compound and then calcining the polyvalent metal sulfate. A method for removing nitrogen oxides in exhaust gas, which comprises contacting a catalyst comprising a salt or a fourth-period transition metal salt supported with exhaust gas containing nitrogen oxides. 2. A method for removing nitrogen oxides in exhaust gas, which comprises contacting the catalyst with exhaust gas containing nitrogen oxides under the above conditions, and then contacting the exhaust gas with an oxidation catalyst. .